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News & Media

Caulerpa seaweed - bag it, bin it.

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Some information from Biosecurity New Zealand on how you can protect the coastal waters we all love from the invasive seaweed exotic caulerpa

A battle is underway at sea this summer to contain the rapid growing non-native (exotic) caulerpa seaweed.

This pest has been known to be present in upper North Island waters since 2021 when it was found for the first time at Aotea Great Barrier Island. Since then, it has been found at Ahuahu Great Mercury Island, Te Rāwhiti Inlet in Northland, off Kawau Island and at Waiheke Island.

Exotic caulerpa can spread quickly, forming dense mats in some areas, and potentially affecting native species by competing for space and food.

Caulerpa forms dense mats on the seafloor, out-competing local flora and fauna. Photo credit - NIWA

Biosecurity New Zealand, in partnership with mana whenua, local authorities, Department of Conservation and local communities is working to manage the situation and is calling on those who work and play at sea to help stop it spreading.

Exotic caulerpa can move over short distances when it breaks into small pieces which are then carried on water movements to new locations. It can move over long distances (and this is how it may have arrived here in New Zealand) by getting tangled in vessel anchors and anchor chains, and fishing and diving gear and then being carried to other areas.

There are some simple actions fishers, boaties and divers can take to ensure they don’t move this pest around as they enjoy the waters this summer.

  • When out on the water, before you move on, check your anchor and chain when you pull it up, and also fishing or diving equipment for any attached seaweed
  • If you find any seaweed on your gear, remove it and bag it or contain it securely so it can’t get back into the water
  • Dispose of it back on shore – in your household rubbish or compost, or in a bin well away from the sea
  • If you can’t do this (securely contain it so it does not get back in the ocean) – put it back into the waters it came from.

There are legal rules (known as a Controlled Area Notice) in place at Aotea Great Barrier Island, Ahuahu Great Mercury Island and Te Rāwhiti Inlet in the Bay of Islands, Northland. In these areas there are legal restrictions on anchoring and some fishing activities. Mana whenua have also placed rāhui in some of these areas with similar restrictions.

Photo credit - NIWA

Exotic caulerpa has also been found at Waiheke Island around Thompson’s Point and Onetangi Bay, and at Kawau Island at Iris Shoal. While there are no legal controls in place, it is best to keep away from these locations.

Before boating, fishing or diving in these three areas, check the Biosecurity New Zealand website for full information on the rules in place: www.biosecurity.govt.nz/caulerpa

This web page has the most up to date information including maps of where exotic caulerpa is, legal controls, rāhui and photos to help you identify it.

We also encourage people to report suspected sightings of exotic caulerpa – either at sea or washed up on the beach.

Caulerpa is relatively easy to identify when washed up on the shore. Do not move caulerpa if you find on the shoreline. Please report it on the links or phone numbers below. Image credit Sid Wales, Biosecurity New Zealand

You can let us know online at report.mpi.govt.nz or by phoning 0800 80 99 66.

If it’s on the shore, don’t move it. We’re not asking people to take any beach-cast home for disposal. Nature will manage this. But we’d still like it to be reported through our phone or web site.

Visit: www.biosecurity.govt.nz/caulerpa

Remember - Out at sea? See weed? Bag it. Bin it.

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